Audio Factory: update

By Wednesday of this week all the BBC's radio networks will be rolled out on to Audio Factory.

That is 11 national services, 6 Nations services and 40 local radio stations. We have also begun switching off our old infrastructure. This switch off will be causing some inconvenience to listeners. We always seek to minimise disruption so it is worth re-stating why these changes have been made.

Before Audio Factory, BBC internet audio streams were provided by different systems and suppliers. All of these disparate systems have reached their end of life. The hardware is, in some cases literally, rusting, and the software that is running the encoding is no longer supported by the companies that wrote it.

Also, the disparate systems meant that listeners would receive a different quality of service depending on which radio station you were listening to. On demand streams for the Nations were not available on Android devices, local radio was in mono, Radio Five Live was at a lower bit rate to Radio 4.

Audio Factory was designed to keep our services available, make them more resilient and ensure a consistent experience. This has required an approach of standardisation. We have chosen http streaming methods to deliver the audio that are robust and are supported by multiple CDN partners. All our services are now available in HLS and HDS using the AAC codec. By the summer we hope to have these streams available in the non-proprietary DASH format.

Sadly, we cannot afford to support every service on all the existing legacy formats. We are now retiring Windows Media. This already had low listener numbers and is not being supported by the wider industry.

We are retiring our SHOUTcast streams that use the AAC codec. The AAC SHOUTcast streams were only available for the national networks. They were provided using the same old unsupported infrastructure that provided the windows media streams for the national networks. SHOUTcast is also our biggest overhead in terms of support. They are only served by a single CDN which makes them vulnerable to outages. To reproduce these SHOUTCAST streams in Audio Factory in multiple codecs and bit rates would have been costly. For these reasons, we are concentrating our efforts around HLS, HDS and DASH.

We have retained a single SHOUTcast stream of each service using the mp3 codec to support devices that cannot support these protocols. This is a fallback for devices that previously consumed windows media or SHOUTcast so our choices around these streams have been to keep them compatible with the widest range of devices. Up to a third of these older devices do not have support for the AAC codec. We believe most of these devices will have support for mp3 streams.

We have been communicating our plans to manufacturers and aggregators for the last 12 months but we are aware that some devices will not be able to receive these new formats, or there may be gaps in service as manufacturers work to deliver upgrades to devices to make them compatible with our new streams. We will continue to work with them to provide the best service we can.

These are still very early days for Audio Factory and we have been very focussed on getting the service live. There are still some local stations in mono, and our full range of bit rates and delivery methods have yet to be rolled out. As we continue to develop the service we will carefully monitor our services and their usage to provide the best quality and value.

Jim Simmons is Senior Product Manager, Audio Services, BBC Radio and Music